Not Applicable
Not Applicable
1. Field of the Invention
The present invention relates to optical measurement devices and particular, to interferometers.
2. Related Arts
U.S. Pat. No. 4,509,858 to Smythe et al, dated Apr. 9, 1985 and entitled xe2x80x9cCompact, Linear Measurement Interferometer With Zero Abbe Errorxe2x80x9d, comprises a light source 11, a detector 12 and a beam splitter 13. The beam splitter divides a beam of light from the source into a test beam and a reference beam. There is a retroreflector in the path of the reference beam and a separate retroreflector in the path of the test beam. The second retroreflector is mounted on a probe 15 which passes through the beam splitter and which can rest on a work piece 17 that is mounted on a table 16. The source 11, detector 12, beam splitter 13 and retroreflector 14 are all mounted on a base that is sturdily positioned over measuring table 16 (see column 3, lines 22-24). The mounting table 16 is usually made of granite or ceramic or the like so that the force of the measurement probe does not deflect the workpiece and the reference holder down-wardly when the measurement probe makes contact with the workpiece Any such downward deflection will cause a significant measurement error. The Smyfte et al Patent also requires a central aperture 20 in the beam splitter 13 through which probe 15 can move (see column 2, line 66 to column 3, line 7).
U.S. Pat.4,924,477 to Gilmore et a1, dated May 8, 1990 and entitled xe2x80x9cAssembly And Method For Determining the Coefficient Of Thermal Expansion Of A Workpiecexe2x80x9d, discloses an apparatus for measuring the coefficient of thermal expansion (CTE) of a workpiece of known length (see column 5, line 50 through column 6, line 36). Th apparatus requires a dual channel light Source and reflectors situated at both ends of the workpiece. The two light signals are directed towards the first reflector, which reflects one signal but passes the other to the second reflector, from which it is reflected. A temperature control system is used to vary the temperature of the workpiece to cause thermal expansion and the CTE is determined by changes in measured light frequencies caused by relative doppler frequency shifts of the reflectors as the workpiece changes in length (see column 6, lines 1-36). As described at column 4, lines 31-36, the assembly has a flexure system so that a workpiece undergoing expansions and contractions during testing can flex causing the image devices (36 and 38 in FIG. 3) to move. This assembly is used to measure the expansion and contraction of a workpiece with a flexure system, so that the coefficient of expansion of the workpiece can be determined. The flexure system only allows for a small amount of movement and is not suitable for measurement of relatively long workpieces. This assembly additionally has laser beam around the sides of the workpiece with imaging devices on both sides of the workpiece. This arrangement leads to a small amount of Abbe error since the measurement path is not directly in line with the gauging points.
The present invention provides a measurement interferometer comprising a frame structure on which is mounted a laser source that emits a source beam, a detector, a beam splitter, a reference retroreflector, a test retroreflector and a reference holder. The invention is characterized in that the beam splitter and the reference holder are interconnected in fixed mutual relation by a connector to constitute a splitter-holder assembly, the beam splitter is positioned to receive a light beam from the laser source and emit a test bean and a reference beam split from the source beam, the reference retroreflector is positioned at a fixed distance from the beam splitter to receive the reference beam from the beam splitter, and in that the test retroreflector is positioned to receive the test beam from the beam splitter and is movable on the frame structure relative to the splitter-holder assembly.
According to another aspect of the invention, the beam splitter is connected to the reference holder by a composite rod. Optionally, the test retroreflector may carry a probe comprising a carbon composite rod as well.
According to yet another aspect of the invention, the reference retroreflector may be in with the beam splitter.
Still another aspect of this invention provides that there may be vibration-dampering member between the splitter-holder assembly and the frame structure.